1. Field of the Invention
The present invention is generally directed to the method and design of mechanical interlock linkages for electrical equipment. More particularly, the present invention is directed to an improved interlock linkage for use in a handle/switch/contactor combination as applied to high powered electric motors. The improved interlock design and method greatly improves reliability, defects per million opportunities, part count, and manufacturing costs.
2. Prior Art
The present invention is an improvement over the prior art. Specifically U.S. Pat. No. 5,424,911 to Joyner et al. disclosed a compact motor controller assembly. Motor controller equipment generally includes so-called xe2x80x9chigh voltagexe2x80x9d motor contactors such as described within U.S. Pat. No. 3,198,910 entitled xe2x80x9cElectromagnetic Relay Having Removable Contact and Coil Assembliesxe2x80x9d as well as xe2x80x9clow voltagexe2x80x9d equipment in the form of relays and the like. One such relay being that described within U.S. Pat. No. 5,057,962 entitled xe2x80x9cMicroprocessor Based Protective Relay System.xe2x80x9d
The motor controller equipment is interlocked with the externally accessible handle operator to prevent access to the high voltage equipment when the operating handle is in the ON position. U.S. Pat. No. 4,760,220 entitled xe2x80x9coperator Mechanism Having reduced Handle Throw and Improved Handle Lockxe2x80x9d is one example of such an interlock.
The state of the art of such motor controller equipment is to mount the low voltage equipment in cabinets having a separate access door from that of the high voltage contactor within a separate compartment to allow ready access to the low voltage equipment without having to turn off the contactor. U.S. Pat. No. 3,621,339 entitled xe2x80x9cModular High Voltage Electrical Components Cooperating Within Cabinet Housing to Provide Electrical Insulation and Cooling Air Passagexe2x80x9d describes the separate arrangement of the high voltage contactors and low voltage equipment.
Therefore it has been determined that a need exists for an improved design of the interlock which increases reliability, lowers part count and manufacturing costs, all while improving operability.
In accordance with a preferred embodiment of the present invention, an interlock mechanism for preventing or enabling the operation of a handle operator or a contactor in certain circumstances comprises a system of mechanical linkages which interact to determine whether a lock-out mode or an enabling mode exists with respect to the electric motor being controlled. A handle operator controls a switch which makes or breaks power to the contactor. Once the contactor has been supplied power by the switch, the contactor may then be commanded to supply and remove electric power to and from the electric motor. If the contactor is supplying power to the electric motor, the contactor activates a contactor pawl assembly to initiate a handle lock-out mode. The contactor pawl assembly displaces a lock-out bar in a linear manner which causes the handle operator to be locked-out. In the handle assembly, the lock-out bar has a circular aperture that receives a push rod in the enable mode and blocks the push rod in the lock-out mode. The push rod is connected to a blocking bracket which must be depressed by a human operator prior to cycling the handle operator. If the blocking bracket cannot be fully depressed by the human operator because the push rod is blocked by the lock-out bar, then the human operator can not cycle the handle operator between its OFF and ON positions, thus a first half of the interlock is achieved. Conversely, the interlock is also designed to prevent the contactor from supplying power to the electric motor if the handle operator is being cycled. If the switch has been closed (handle operator is in the ON position) and power has been supplied to the contactor but not yet to the electric motor, and the blocking bracket has been activated successfully such that the push rod has engaged the lock-out bar, then the contactor pawl assembly is unable to move and thus the contactor cannot be command to supply power to the electric motor. Thus a two way mechanical interlock is achieved.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.